This disclosure relates to novel aqueous dispersions of colorants and polyurethane dispersants containing cross-linkable moieties, the cross-linked polyurethane dispersants that produce the stable aqueous colorant dispersions, the process of making same and the use thereof in ink-jet.
Aqueous dispersions of pigment particles are widely used in ink-jet printing. Because a pigment is typically not soluble in an aqueous vehicle, it is often required to use a dispersing agent, such as a polymeric dispersant or a surfactant, to produce a stable dispersion of the pigment in the aqueous vehicle. However, because the pigment is dispersed in a liquid vehicle, there is a tendency for pigment particles to agglomerate or flocculate while the ink is being stored or while the ink is being used, for example, being printed.
There has been effort in the art directed at improving the stability of pigment dispersions. The effort to improve dispersion stability to date has included improvements in the processes used to make the dispersions, the development of new dispersants and the exploration of the interaction between dispersants and pigment particles, and between dispersants and aqueous vehicle. While much of the effort has general application at improving dispersion stability, some of that effort has not found utility in particular applications. For example, the pigment dispersions used in ink-jet printing applications have very unique and demanding requirements. It is critical that ink components comprising pigment dispersion remain stable, not only in storage but also over repeated jetting cycles. It is also desirable that the pigment dispersions offer good durability, good rub-fastness, wet-fastness and highlighter pen fastness.
A need exists for highly stable, higher-quality and different property inks for ink-jet applications. Although improvements in polymeric dispersants have significantly contributed to improved ink-jet inks, the current dispersants still do not provide inks with the requisite stability, durability, optical density and chroma needed for ink-jet applications. The present invention satisfies this need by providing a cross-linked pigment dispersion based on a polyurethane dispersant having cross-linkable moieties both pendent to the polymer backbone and terminal to the polymer chain, and the cross-linking of these moieties with a cross-linking agent.